1. Field of the Invention
The present invention relates generally to a multi-layered golf ball having an inner core, at least one intermediate layer, and an outer cover, wherein the intermediate layer is made from a polyurea composition. More particularly, the polyurea composition contains ultra-high molecular weight polyethylene (UHMWPE) powder particulate dispersed therein.
2. Brief Review of the Related Art
In recent years, golf balls having a multi-layered design have become more common. For example, three-piece balls having an inner core, at least one intermediate layer surrounding the core, and an outer cover have been developed. Different materials are used to make each of these layers in effort to impart more desirable playing performance properties to the golf ball. Referring to FIG. 1, a golf ball (10) having a conventional three-piece design is shown. The ball (10) includes an inner core (12) that may be, for example, solid, semi-solid, fluid-filled, or hollow. A variety of materials may be used to make the core, particularly natural and synthetic rubbers such as styrene butadiene, polybutadiene, isoprene, polyisoprene, and trans-isoprene. In one version, as shown in FIG. 1, the core (12) is a single-piece made from a natural or synthetic rubber composition such as polybutadiene. In other instances, as shown in FIG. 2, the golf ball (10a) contains a two-piece core; that is, there are two core pieces (12a, 14). For example, an inner core portion (12a) may be made of a first base rubber material and an outer core layer (14), which surrounds the inner core (12a), may be made of a second base rubber material. Cross-linking agents and fillers may be added to the rubber materials. The respective core portions (12a, 14) may be made of the same or different rubber materials. The multi-layered core (constituting inner and outer core layers (12a, 14)) may be referred to as the “center” of the ball.
In FIGS. 1 and 2, each respective ball (10, 10a) is shown having an intermediate layer (16, 16a). As used herein, the term, “intermediate layer” means a layer of the ball disposed between the core and cover. The intermediate layer may be considered an outer core layer or inner cover layer or any other layer disposed between the inner core and outer cover of the ball. The intermediate layer also may be referred to as a casing or mantle layer. It further should be understood that the ball may include one or more intermediate layers. In conventional golf balls (10, 10a), the intermediate layer (16, 16a) may be made of ionomer resins. These cross-linked polymers contain inter-chain ionic bonding as well as covalent bonding. The ionomer resins include, for example, a copolymer of ethylene and a vinyl comonomer with an acid group such as methacrylic or acrylic acid. Metal ions such as sodium, lithium, zinc, and magnesium are used to neutralize the acid groups in the polymer. Commercially available ionomer resins are known in the industry and include numerous resins sold under the trademarks, Surlyn® (DuPont) and Escor®D and Iotek® (Exxon). These ionomer resins are available in various grades and are identified based on the type of base resin, molecular weight, type of metal ion, amount of acid, degree of neutralization, additives, and other properties.
Lastly, each of the conventional balls (10, 10a) shown in FIGS. 1 and 2 includes an outer cover layer (18, 18a) designed to have high durability, abrasion-resistance, impact-resistance, resiliency, and other desirable properties. The golf balls (10, 10a) can comprise one or more cover layers (18, 18a). Different materials may be used to make the cover layer (18, 18a) including the above-described ionomer resins. The covers (18, 18a) provide the balls with desirable durability and rebounding properties. The rebound performance of the golf ball is based on initial velocity of the ball after being struck by a golf club and its outgoing velocity after making impact with a hard surface. In general, golf balls having a harder outer cover tend to have higher rebound performance. Other materials can be used to make the cover including, for example, polyurethane, polyurea, and polyurethane/polyurea hybrid compositions. These polyurethane and/or polyurea compositions can be used to help provide the player with a better “feel” when he/she strikes the ball with the club face. Players may hear a pleasant “clicking” sound as the club face makes impact with the outer cover of these balls. In addition, the softer feel of the ball cover allows players to place a spin on the ball and better control its flight direction.
As discussed above, polyurethane and polyurea compositions provide the ball with desirable softness and improved playing performance properties. Golf players may experience a better sensation when striking a golf ball having a cover made of polyurethane and polyurea compositions. Because of these advantageous properties, it has been proposed in certain instances that polyurethane and polyurea materials be used to make intermediate casing or mantle layers that surround the golf ball core as well as the outer cover layer.
For example, Wu et al., U.S. Pat. No. 7,202,303 discloses a golf ball including a cover, core, and at least one intermediate layer interposed between the cover and core. The compositions used for the different layers can be polyurethane-based compositions incorporating block copolymers, polyurea-based compositions incorporating block copolymers, and mixtures thereof. The compositions may be formed by reacting excess prepolymer, which is based on an isocyanate and a polyol or amine, with a functionalized block copolymer to form an intermediate prepolymer having the block copolymer portion capped with isocyanate groups at each end. This prepolymer is then reacted with a curing agent to form a polyurethane-based or polyurea-based composition.
Bulpett et al., U.S. Pat. No. 6,964,621 discloses a multi-layered golf ball having an inner core, at least one intermediate layer, and an outer cover, wherein the cover is made from a polyurea composition, preferably saturated and/or water resistant. The polyurea composition is made from a polyurea prepolymer and curing agent, wherein the polyurea prepolymer includes an isocyanate and amine-terminated compound. The '621 patent also discloses that the polyurea composition may be used to form the intermediate layer.
Nardacci, U.S. Pat. No. 6,884,182 discloses a golf ball comprising: a core; a cover; and at least one intermediate layer disposed between the cover and core. The intermediate layer is formed of a composite of binding material and interstitial fiber material. The interstitial fiber material is radially oriented in the intermediate layer and symmetrically distributed. Preferably, the fiber material is oriented so that a central axis of the fiber material is co-axial with a radius line of the ball. Preferably, the fiber material is positioned such that it has spherical symmetry with the ball. In one embodiment, the fiber material may extend from the intermediate layer into the core.
Sullivan et al., U.S. Pat. No. 6,612,939 discloses golf balls having an outermost polymeric cover; one or more mantle layers; and an inner core material. The mantle layer(s) may be formed of metal, ceramic, or composite materials. The metals used in the mantle layer are preferably steel, titanium, chromium, nickel, or alloys thereof. If ceramic layers are desired, they can be made of such materials as silica, soda lime, lead silicate, borosilicate, aluminoborosilicate, aluminosilicate, and various glasses. The ceramics can be reinforced with silicon carbide, glass and/or carbon fibers. A composite mantle layer also can be prepared from a composite material of glass fibers dispersed within a thermoset matrix such as a polyimide material, silicone, vinyl ester, polyester, or melamine. In other embodiments, glass or carbon fibers may be dispersed within a nylon matrix. The golf balls, according to the '939 patent, show improved spin, feel, and acoustic properties.
However, one problem with using conventional polyurea compositions in intermediate casing layers is the finished layer may show poor impact-resistance. Particularly, this may be a problem when golf ball manufacturers try to increase the hardness of a casing layer made with a polyurea composition in order to make it comparable to the hardness of a casing layer made with ionomer resin. That is, the polyurea composition may be formulated to have increased hardness but this may be offset by the polyurea formulation showing decreased impact-resistance. The resulting golf ball may have desirable hardness properties but appear damaged and worn after only limited use, because of its low impact-resistance.
Thus, it would be desirable to develop a golf ball containing an intermediate casing layer made of a polyurea composition having sufficient hardness and impact-resistance. The improved casing layer would provide the ball with a combination of good durability and toughness as well as optimum playing performance properties such as feel, softness, spin control, and the like. The present invention provides golf balls having such intermediate casing layers.